1. Field of the Invention
The present invention relates to an exposure apparatus, an exposure method, a device manufacturing method.
2. Description of the Related Art
Exposure apparatuses exposes a pattern of an original (reticle or the like) onto a photosensitive substrate (e.g., wafer or the like where the surface thereof is coated with a resist layer) via a projection optical system in a lithography step included in manufacturing steps for semiconductor devices, liquid crystal display devices, and the like. Among them, in particular, a step-and-scan type exposure apparatus performs exposure while synchronously scanning an original and a substrate. An area to be exposed by a single scanning exposure on a substrate is referred to as a “shot” (pattern forming area), and an exposure apparatus sequentially exposes a plurality of shots preset on a substrate. Note that the projection magnification of a projection optical system which may be employed in such an exposure apparatus is typically ¼. Hereinafter, an exposure apparatus including a projection optical system having a ¼ projection magnification is referred to as a “¼ projection exposure apparatus”.
Here, one of performances required for such exposure apparatuses is superimposing accuracy. In order to improve the superimposing accuracy, it is required that an original and a substrate are synchronously scanned with high accuracy. Japanese Patent Laid-Open No. 2000-228344 discloses a scanning exposure apparatus that corrects the target position of an original or a substrate depending on the scan position in a shot in order to improve superimposing accuracy (mix-and-match accuracy) between different exposure apparatuses.
In addition, an error may occur on the arrangement state of shots had subjected to one-time exposure, and thus, it is desirable that a step position is corrected in advance by measuring the arrangement state of shots based on the positions of the shots formed on a substrate. Such correction (measurement) is typically referred to as “global alignment measurement (AGA measurement)”. Furthermore, there is an exposure apparatus (hereinafter referred to as “½ projection exposure apparatus”) having a small reduction magnification, which employs, for example, a ½ projection optical system, for the improvement in throughput thereof. Upon exposure of the original having the same size as that of the original exposed by, for example, the ¼ projection exposure apparatus, the ½ projection exposure apparatus can expose a larger area on a substrate by a single scanning exposure, resulting in a reduction in scanning exposure times and a further improvement in throughput.
However, when mix-and-match is performed between the ½ projection exposure apparatus and the ¼ projection exposure apparatus, a superimposing error may occur due to the difference in size of shots for exposure between the exposure apparatuses. For example, in the ¼ projection exposure apparatus, two shot areas exposed by double scanning through the intermediary of stepwise movement may include a step error. In contrast, the ½ projection exposure apparatus exposes the same areas by a single scanning, resulting in no occurrence of a step error. Due to the presence of such a difference, i.e., due to the occurrence of an error caused by mix-and-match between exposure apparatuses (e.g., the ½ projection exposure apparatus and the ¼ projection exposure apparatus) having different projection magnifications, it is difficult to superimpose (overlay) an original on a substrate with high accuracy.